NAME
Data::UUID::NCName - Make valid NCName tokens which are also UUIDs
VERSION
Version 0.01
SYNOPSIS
use Data::UUID::NCName qw(:all);
my $uuid = '1ff916f3-6ed7-443a-bef5-f4c85f18cd10';
my $ncn = to_ncname($uuid);
# $ncn is now "EH_kW827XQ6vvX0yF8YzRA".
# from Test::More, this will output 'ok':
is(from_ncname($ncn), $uuid, 'Decoding result matches original');
DESCRIPTION
The purpose of this module is to devise an alternative representation of
the UUID which conforms to the constraints of various other identifiers
such as NCName, and create an isomorphic mapping between them.
RATIONALE & METHOD
The UUID is a generic identifier which is large enough to be globally
unique. This makes it useful as a canonical name for data objects in
distributed systems, especially those that cross administrative
jurisdictions, such as the World-Wide Web. The representation, however,
of the UUID, precludes it from being used in many places where it would
be useful to do so.
In particular, there are grammars for many types of identifiers which
must not begin with a digit. Others are case-insensitive, or prohibited
from containing hyphens (present in both the standard notation and
Base64URL), or indeed anything outside of `^[A-Za-z_][0-9A-Za-z_]*$'.
The hexadecimal notation of the UUID has a 5/8 chance of beginning with
a digit, Base64 has a 5/32 chance, and Base32 has a 3/16 chance. As
such, the identifier must be modified in such a way as to guarantee
beginning with an alphabetic letter (or underscore `_', but some
grammars even prohibit that, so we omit it as well).
While it is conceivable to simply add a padding character, there are a
few considerations which make it more appealing to derive the initial
character from the content of the UUID itself:
* UUIDs are large (128-bit) identifiers as it is, and it is
undesirable to add meaningless syntax to them if we can avoid doing
so.
* 128 bits is an inconvenient number for aligning to both Base32 (130)
and Base64 (132), though 120 divides cleanly into 5, 6 and 8.
* The 13th quartet, or higher four bits of the
`time_hi_and_version_field' of the UUID is constant, as it indicates
the UUID's version. If we encode this value using the scheme common
to both Base64 and Base32, we get values between `A' and `P', with
the valid subset between `B' and `F'.
Therefore: extract the UUID's version quartet, shift all subsequent data
4 bits to the left, zero-pad to the octet, encode with either
*base64url* or *base32*, truncate, and finally prepend the encoded
version character. Voilà, one token-safe UUID.
APPLICATIONS
XML IDs
The `ID' production appears to have been constricted, inadvertently
or otherwise, from Name in both the XML 1.0 and 1.1 specifications,
to NCName by XML Schema Part 2. This removes the colon character `:'
from the grammar. The net effect is that
while being a *well-formed* ID *and* valid under DTD validation, is
*not* valid per XML Schema Part 2 or anything that uses it (e.g.
Relax NG).
RDF blank node identifiers
Blank node identifiers in RDF are intended for serialization, to act
as a handle so that multiple RDF statements can refer to the same
blank node. The RDF abstract syntax specifies that the validity
constraints of blank node identifiers be delegated to the concrete
syntax specifications. The RDF/XML syntax specification lists the
blank node identifier as NCName. However, according to the Turtle
spec, this is a valid blank node identifier:
_:42df00ec-30a2-431f-be9e-e3a612b325db
despite an older version listing a production equivalent to the more
conservative NCName. NTriples syntax is even more constrained, given
as `[A-Za-z][0-9A-Za-z]*'.
Generated symbols
There are only two hard things in computer science: cache
invalidation and naming things [and off-by-one errors].
-- Phil Karlton [extension of unknown origin]
Suppose you wanted to create a literate programming system (I do).
One of your (my) stipulations is that the symbols get defined in the
*prose*, rather than the *code*. However, you (I) still want to be
able to validate the code's syntax, and potentially even run the
code, without having to commit to naming anything. You are (I am)
also interested in creating a global map of classes, datatypes and
code fragments, which can be operated on and tested in isolation,
ported to other languages, or transplanted into the more
conventional packages of programs, libraries and frameworks. The
Base32 UUID NCName representation should be adequate for placeholder
symbols in just about any programming language, save for those which
do not permit identifiers as long as 26 characters (which are
extremely scarce).
EXPORT
No subroutines are exported by default. Be sure to include at least one
of the following in your `use' statement:
:all
Import all functions.
:decode
Import decode-only functions.
:encode
Import encode-only functions.
:32 Import base32-only functions.
:64 Import base64-only functions.
SUBROUTINES
to_ncname $UUID [, $RADIX ]
Turn `$UUID' into an NCName. The UUID can be in the canonical
(hyphenated) hexadecimal form, non-hyphenated hexadecimal, Base64
(regular and base64url), or binary. The function returns a legal NCName
equivalent to the UUID, in either Base32 or Base64 (url), given a
specified `$RADIX' of 32 or 64. If the radix is omitted, Base64 is
assumed.
from_ncname $NCNAME [, $FORMAT, $RADIX ]
Turn an appropriate `$NCNAME' back into a UUID, where *appropriate*,
unless overridden by `$RADIX', is defined beginning with one initial
alphabetic letter (A to Z, case-insensitive) followed by either:
25 Base32 characters, or
21 Base64URL characters.
The function will return `undef' immediately if it cannot match either
of these patterns. Input past the 21-character mark (for Base64) or
25-character mark (for Base32) is ignored.
This function returns a UUID of type `$FORMAT', which if left undefined,
must be one of the following:
str The canonical UUID format, like so:
`33fcc995-5d10-477e-a9b4-c9cc405bbf04'. This is the default.
hex The same thing, minus the hyphens.
b64 Base64.
bin A binary string.
to_ncname_64 $UUID
Shorthand for Base64 NCNames.
from_ncname_64 $NCNAME [, $FORMAT ]
Ditto.
to_ncname_32 $UUID
Shorthand for Base32 NCNames.
from_ncname_32 $NCNAME [, $FORMAT ]
Ditto.
AUTHOR
Dorian Taylor, `'
BUGS
Please report any bugs or feature requests to `bug-data-uuid-ncname at
rt.cpan.org', or through the web interface at
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Data-UUID-NCName. I will
be notified, and then you'll automatically be notified of progress on
your bug as I make changes.
SUPPORT
You can find documentation for this module with the perldoc command.
perldoc Data::UUID::NCName
You can also look for information at:
* RT: CPAN's request tracker (report bugs here)
http://rt.cpan.org/NoAuth/Bugs.html?Dist=Data-UUID-NCName
* AnnoCPAN: Annotated CPAN documentation
http://annocpan.org/dist/Data-UUID-NCName
* CPAN Ratings
http://cpanratings.perl.org/d/Data-UUID-NCName
* Search CPAN
http://search.cpan.org/dist/Data-UUID-NCName/
SEE ALSO
Data::UUID
OSSP::uuid
RFC 4122
RFC 4648
Namespaces in XML (NCName)
W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes (ID)
RDF/XML Syntax Specification (Revised)
Turtle
This module lives under the `Data::' namespace for the purpose of
hygiene. It *does not* depend on Data::UUID or any other UUID modules.
LICENSE AND COPYRIGHT
Copyright 2012 Dorian Taylor.
Licensed under the Apache License, Version 2.0 (the "License"); you may
not use this file except in compliance with the License. You may obtain
a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 .
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.